sedimentary
Chert (specifically Green Chert/Jasper)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 6.5–7 (Mohs scale); Color: Olive green to grayish-green; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.65.
- Hardness
- 6
- Color
- Olive green to grayish-green
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Olive green to grayish-green; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary layers. This weathered pebble likely dates from various geological eras depending on its parent outcrop.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp conchoidal edges; currently used for geological collecting, aquarium gravel, and occasionally lapidary work (tumbling/polishing).
Geological facts
Chert is so tough and chemically stable that it often survives as rounded pebbles in riverbeds long after the surrounding rock has eroded. Green varieties usually get their color from iron silicates or chlorite inclusions.
Field identification & locations
Identify in the field by its waxy texture, inability to be scratched by a steel knife, and characteristic 'shell-like' curved breaks. Commonly found in riverbeds, glacial tills, and coastal beaches.
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